Peristaltic hose pumps of the construction mentioned above are known in various variants. There are in principle two basic concepts. The first basic concepts that the hose Arranged around the roller wheel is pressed by means of pressure arched element or the like against the roller wheel. Such embodiments are for instance known from the documents U.S. Pat. No. 4,798,580 and U.S. Pat. No. 5,044,902. The second basic concept, on which the invention is based, consists in that the elastic hose is pulled by a tensile force of suitable size with a sufficient angle of wrapping, typically more than 90° and less than 270°, in most cases in the range from 150° to 220°, around the roller wheel. Thereby, a pressure arched element or the like is not necessary. The tensile force is dimensioned according to the elastic properties of the hose such that in the region of a roller of a roller wheel, the interior cross-section of the hose is reduced to practically zero. By rotation of this region with the roller about the roller wheel axis, the feed of the fluid in the hose is effected. Examples are described in the documents U.S. Pat. No. 4,537,561 and U.S. Pat. No. 5,213,483. A particularly advantageous variant of the second basic concept is described in the document DE 19960668 A1.
It is common to all above peristaltic hose pumps that across a broad range there is a nearly linear correlation between the speed of the roller wheel and the flow, and in fact independently from the generated pressure respectively counter-pressure. In these connections it is however also known that with very high pressures respectively counter-pressures, typically above 530 mbar, the correlation between speed and flow becomes non-linear.
When using peristaltic hose pumps in the field of medicine, for instance for generating a flow through a body cavity by introduction of a medical instrument, which is fed by means of the peristaltic hose pump with fluid, the pressure respectively counter-pressure is a critical parameter. A doctor wishes on the one hand a high flow for rinsing the body cavity. On the other hand, a certain pressure is in fact desirable for expanding the body cavity, this pressure is however also a very critical parameter. Approx. 500 mbar, better 400 mbar, should definitely not be exceeded. Typical pressures, which are medically harmless, are in the range from approx. 50 to 300 mbar.
For peristaltic hose pumps of prior art construction, comprehensive safety measures are provided, in order to safely prevent an inadmissible pressure rise in a body cavity when adjusting a high flow. Typically, a pressure sensor is provided, which regularly monitors the pressure in the body cavity and/or the feed line to the medical instrument respectively the pressure side of the peristaltic pump and adjusts the drive of the roller wheel to smaller speeds, if the pressure is too high. It is even possible that the roller wheel is adjusted to reverse operation in the case of a strong pressure rise in the body cavity. This will in particular take place, when an inadmissibly high pressure could occur at a very small flow already.
The above measurement and control measures are all in all expensive, thus prior art peristaltic hose pumps being costly. It would be desirable to provide a peristaltic hose pump for use in the field of medicine, the roller wheel speed of which is preselectable and otherwise constant, and in which a defined limit pressure cannot be exceeded for any of the preselectable speeds, and in fact without the necessity of suitable pressure sensors and control of the speed of the roller wheel.